Correct, but if the Vampire standalone mainboard would have parameters of A1200 PCB (holes, ports placement etc) which are known, it will easily fit into this new case.

AFAIK, no design work has yet been done on a Vampire standalone, but I think it's pretty unlikely that it would be an A1200 PCB - if it was, there would be about 90% of the board empty. Even miniITX would be a pretty empty board!